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Industrial Crops and Products 52 (2014) 74– 84

Contents lists available at ScienceDirect

Industrial Crops and Products

journa l h om epa ge: www.elsev ier .com/ locate / indcrop

ovel poly(alkyd-urethane)s from vegetable oils: Synthesis androperties

em Shan Linga, Issam Ahmed Mohammedb,∗,1, Arniza Ghazali a, Melati Khairuddeanc

School of Industrial Technology, Universiti Sains Malaysia, 11800 Penang, MalaysiaDepartment of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 Serdang, Selangor, MalaysiaSchool of Chemical Science, Universiti Sains Malaysia, 11800 Penang, Malaysia

r t i c l e i n f o

rticle history:eceived 26 June 2013eceived in revised form 2 October 2013ccepted 3 October 2013

eywords:lkydrethanealm oilharacterization

a b s t r a c t

Triglycerides of palm (Elaeis guineensis) oil, soy (Glycine max) oil and sunflower (Helianthus annuus) oilwere converted to monoglycerides by glycerolysis process. The monoglycerides derived from the differ-ent oils were reacted with phthalic anhydride at 2:1 monoglyceride-to-phthalic anhydride ratio to obtainnovel polyols called alkyd diols. The polyols were reacted with 4,4′-methylenediphenyldiisocyanate(MDI) to produce five novel poly(alkyd-urethane)s (PAU), namely palm oil based poly(alkyd-urethane)(POPAU), soy oil based poly(alkyd-urethane) (SOPAU), sunflower oil based poly(alkyd-urethane)(SFPAU), palm-soy oils based poly(alkyd-urethane) (POSOPAU) and palm-sunflower oils basedpoly(alkyd-urethane) (POSFPAU). The successful synthesis of the monoglycerides, alkyd diols andpoly(alkyd-urethane)s were confirmed by FTIR, 1H NMR, 13C NMR spectroscopy and their morphology

erformance were evaluated by scanning electron microscopy (SEM). Further analyses included viscosity, solubility,iodine number testing, gel content, drying time test, thermogravimetric analysis (TGA), crosshatch adhe-sion tests, impact strength, pencil hardness, chemical and water resistance. Palm oil poly(alkyd-urethane)showed good thermal stability with only 5% weight loss temperature in nitrogen at 270 ◦C. Improvementsin coating performance after blending with sunflower oil or soy oil based alkyd-diols were also observed.

. Introduction

In the last decade, the depletion of crude oil and increasingil price have pushed scientists to turn to eco-friendly and cost-ffective materials while investigating renewable natural materialss an alternative source of monomers in the manufacturing of poly-er (Patel et al., 2008). Vegetable oils are one of the sustainableaterials known to be utilized and would usually go through vari-

us chemical functionalizations (Khot et al., 2001; Hu et al., 2002;anaka et al., 2007; Mosiewicki et al., 2009a,b) in various polymerynthesis processes.

Alkyd resins are tough resinous polymeric materials preparedia an esterification reaction between polybasic acids, polyolsnd monoacids (commonly fatty acids from vegetable oils or

ats) (Parker, 1965). They are widely used and constitute about0% of the conventional binders used in surface coatings todayHlaing and Oo, 2008) due to their good attributes such as strength,

∗ Corresponding author. Tel.: +60 3684966979.E-mail address: issam@upm.edu.my (I. Ahmed Mohammed).

1 Previously at School of Industrial Technology, UniversitiSains Malaysia, Penang1800, Malaysia.

926-6690/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.indcrop.2013.10.002

© 2013 Elsevier B.V. All rights reserved.

flexibility, gloss retention, good thermal stability and low price.However, it was reported that alkyd resins possess a few weak-nesses such as low water resistance, alkaline resistance and solventresistance (Williams, 2000). In addition, alkyds have to be dilutedin organic solvents prior to application and some of the alkydresins such as palm oil-based alkyd resins take a long time to drydue to their lower level of unsaturation in the fatty acid chain. Tosurmount these problems, previous researches were directed tocopolymerization of alkyd with acrylate monomers (Akintayo andAdebowale, 2004a; Uschanov et al., 2008), inter-esterification withother oil such as Tung oil (Saravari et al., 2005) and modificationswith other chemicals such as natural rubber (Lee et al., 2010a,b).Blending of palm oil based alkyd with other resins such as epoxywas also reported (Issam et al., 2011) to enhance properties ofalkyd resins in terms of morphology, viscosity, adhesion, pendulumhardness and impact strength over individual resins.

Owing to the presence of urethane linkages, polyurethanes onthe other hand, exhibit faster drying time, better abrasion resis-tance, toughness, chemical and UV resistance when compared to

alkyd resins. Extensive applications of polyurethane can be foundin high performance coatings, such as that of automotive appli-ances and wood industries (Poul, 1996; Swaraj, 1997; Jayakumaret al., 2003; Alam et al., 2004; Dutta and Karak, 2005). It is projected

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hat by incorporating urethane linkages into the alkyd backbone, aoly(alkyd-urethane) with enhanced functionality over the indi-idual resins could be produced. To the best of the authors’nowledge, there is no report published on the chemical modifi-ation of alkyds by urethane and the consequent effects.

Thus, a series of novel polymers named poly(alkyd-urethane)sere designed by reacting diisocyanates with alkyd diols from two

f the abundant vegetable oils: palm oil and soy oil. Palm oil isegetable oil derived from fruit of oil palms and was selected dueo its renewability and abundance mainly in the South East Asianountries such as Malaysia, Indonesia and Africa with a produc-ion of 53 metric tons, which occupies 33.98% of total world plantil productions in the year of 2012 (USDA, 2013a). It has recentlyeen much demand and received much attention in the synthe-is of different polymers or their derivatives such as alkyds (Issamnd Cheun, 2009; Ang and Gan, 2012), polyurethanes (Chuayjuljitt al., 2007; Saravari et al., 2007) and bio-diesel fuel (Kalam andasjuki, 2002; Mohamad and Ali, 2002). The world’s most pro-

uced vegetable oil is followed by soybean oil with 27.66% of totalorld’s production (USDA, 2013b) which has been seen utilized in

he development of IPN (interpenetrating elastomeric networks)Athawale and Kolekar, 2000; Raut and Athawale, 2000; Athawalend Pillay, 2001).

With sunflower oil as the benchmark, the outcome of synthe-ized poly(alkyd-urethane)s based on alkyd diol from palm oil andoy oil are hereby discussed with respect to the their relative prop-rties.

. Experimental

.1. Material

All purchased chemicals were used as received. Palm oil,oy oil and sunflower oil were purchased from Tesco StoresdnBhd, Malaysia. Glycerol, toluene and acetone were man-factured by R&M Chemical, UK. Calcium Oxide (CaO) wasbtained from Hamburg Chemicals. Phthalic anhydride and 4,4′-ethylenediphenyldiisocyanate were supplied by Fluka Chemical,ermany while xylene was manufactured by J. T. Baker SOLU-ORB. Ethanol, dimethyl formamide (DMF) and tetrahydrofuranere received from Fisher Scientifik UK Limited. DMF was distilled

ver calcium hydride before use.

.2. Preparation of poly(alkyd-urethane)s

Two distinct steps were involved in preparation of alkyd diols.he first step was the reaction between vegetable triglyceridesnd glycerol. Triglycerides underwent trans-esterification by glyc-rolysis in the presence of catalyst at an elevated temperature,hus forming monoglyceride. The second major step was theransformation of the monoglyceride to diols with the UNRE-CTED and TERMINATED hydroxyl groups by reaction with excesshthalic anhydride. The intrinsic type of this reaction was that,he ring opening of phthalic anhydride did not involve any waternd this occurred readily at temperature of 180 ◦C. The alkydiols were then reacted with the same amount of NCO group of,4′-methylenediphenyldiisocyanate, forming urethane bonding,esulting in the formation of the poly(alkyd-urethane)s or PAUs.

.2.1. Preparation of monoglyceridesA four-necked, round-bottomed flask equipped with mechan-

cal stirrer, reflux condenser, N2 inlet and addition funnel was

harged with 1 equiv. of palm oil and 0.1% CaO powder (byeight) as a catalyst. As the palm oil was heated up to 235 ◦C,

equiv. of glycerol were fed into the system blanketed by nitrogenow. The reaction was allowed to stand for 3 h. The glycerolysis

d Products 52 (2014) 74– 84 75

product, however, may be expected to be consisting majorly of �-monoglyceride (>60%) while minor presence of �-monoglycerides,��′-monoglycerides, ��-diglyceride, triglyceride and glycerol wasunavoidable (Igwe and Ogbobe, 2000). The reaction was continueduntil a satisfactory high amount of conversion of triglyceride into�-monoglyceride was ensured whereby, a little sample of mono-glyceride was taken out by using a glass rod to test its solubilityin ethanol and no emulsion or white spots in the ethanol solutionwere observed. This reaction produced monoglyceride from palmoil (PO-mono) and substituting soy oil or sunflower oil for palmoil would then produce monoglyceride based on soy oil (SO-mono)and sunflower oil (SF-mono), respectively.

2.2.2. Preparation of alkyd diolsA four-necked, round-bottomed flask equipped with mechan-

ical stirrer, Dean-Stark trap, N2 inlet and addition funnel wascharged with 2 equiv. of PO-mono and 10% xylene (based on weightof monoglyceride). 1 equiv. of phthalic anhydride was added as thetemperature of monoglyceride reached 180 ◦C. The temperaturewas controlled at 190 ◦C and the reaction continued for 4 h under anitrogen blanket. Sample was taken periodically to check the acidnumber until it fell below 5 mg KOH g−1. Eventually, water andxylene were removed under pressure. Thus palm oil based alkyddiol (PO-diol) was obtained.

Substituting palm oil monoglyceride with the same equivalentof soy oil monoglyceride or sunflower oil monoglyceride wouldproduce soy oil based (SO-diol) and sunflower oil alkyd diol (SF-diol), respectively.

2.2.3. Synthesis of PAUInto a four-necked, round-bottomed flask equipped with

mechanical stirrer, reflux condenser, N2 inlet and additionfunnel was charged 1 equiv. of PO-diol. 1 equiv. of liquid 4,4′-methylenediphenyldiisocyanate (MDI) with DMF was added intothe reaction flask through the dropping funnel. The reaction flaskwas heated up and maintained at 70 ◦C for 1 h and a half and sub-sequently increased to 110 ◦C. The reaction was continued for 12 hwith a blanket of nitrogen maintained throughout the reaction. Alittle sample of PAU was taken out every 2 h for FTIR inspection untilall diisocyanate was successfully reacted. The solvent, DMF, wasremoved under pressure. POPAU was formed, cooled and furtheranalyzed.

The reaction was repeated in the same manner by substitutingPO-diol with 1 equiv. of SO-diol or SF-diol to produce SOPAU andSFPAU, respectively. For the synthesis of POSOPAU and POSFPAUrespectively, a blend of 0.5 equiv. of PO-diol with 0.5 equiv. of SO-diol or with 0.5 equiv. of SF-diol, was reacted with 1 equiv. of MDIas the way POPAU was produced.

2.3. Instrumentation and measurements

2.3.1. Fourier transform infrared spectroscopic analysisChemical compositions of the monoglycerides, alkyd diols and

PAUs were evaluated by Fourier Transform Infrared (FTIR) in a Nico-let FTIR Avatar 360 using KBr pellet at wavelengths between 4000and 400 cm−1.

2.3.2. 1H and 13C NMR analysis1H and 13C NMR spectra of the monoglycerides, alkyd diols

and PAUs were obtained using Bruker 400 MHz NMR spectrometer,using DMSO-d6 as the solvent and TMS as the internal reference.

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.3.3. Scanning electron microscopy (SEM)The solid samples were gold-sputtered and the morphologies

f PAU resins were studied by SEM using a LEO Supra 50 vP Fieldmission Scanning Electron Microscope (FESEM).

.3.4. ViscosityA HAAKE Rotary Viscometer PK100 was employed for viscosity

etermination of the resins in centipoises unit (cPs) at the temper-ture of 25 ◦C.

.3.5. Acid numberThe acid number of resin was determined procedures based on

STM D1980-87.

.3.6. Hydroxyl valueHydroxyl value of alkyd diols was determined based on ASTM D

849 (Method C).

.3.7. Iodine number testIodine number test was used to determine unsaturated groups

resent in each synthesized PAU. Each sample was repeated threeimes and the calculation for the iodine number was as given below.

eight of PAU sample (∼0.2 g) was placed in the conical flaskarked to the nearest 0.1 mg. The sample was dissolved in 10 mL

hloroform (as solvent) and 40 mL (depending on the standard)odine monobromide “Hanus solution” (a mixture of 13.02 g ofodine and 45 mL bromine was dissolved in 1 L of acetic acid) wasdded into both blank and sample conical flasks marked for 1 h.otassium iodide solution (25 mL) was added to the flask followedy titration to an end point (yellow color) with the standardizedodium thiosulfate solution as indicator, (shaking vigorously whileitrating). The titration was continued after adding 1 mL of starchndicator solution until a clear and colorless solution of pH 1.86 waschieved.

odine number = (V2 − V1) × N(Na2S2O3) × 12.69Weight of sample (g)

here, V2 and V1 represent blank and sample volumes, respectively.

.3.8. Gel contentThe degree of curing for obtained cured was determined by gel

ontent test according to ASTM D2765. Gel content test was deter-ined by Soxhlet extraction using toluene as solvent. The cured

heets were weighed and placed in a cellulose extraction thimblen the Soxhlet’s extractor. Four sets of Soxhlet’s extractor have beensed. The solvent extraction was carried out with 250 mL tolueneor 3 h. After that, the samples were taken out followed by vacuumried and re-weighed until a constant weight was achieved. Gelontent of the coating was calculated according to the followingquation:

el content (%) = Weight after extractionWeight before extraction

× 100

.3.9. Drying time testCoated films with thickness of 120 �m were dried at ambient

emperature (30 ± 0.5 ◦C) under atmospheric condition (70–90%elative humidity) with 3 different amounts of cobalt naphthanates dryer (3%, 4% and 5%).

.3.10. Thermogravimetric analysisThermogravimetric analyses (TGA) on the PAUs were carried

ut in a nitrogen atmosphere with Perkin–Elmer TGA 7 series at0 ◦C min−1. Samples weighed approximately 50 mg.

d Products 52 (2014) 74– 84

2.3.11. Crosshatch adhesion testThe crosshatch adhesion test was performed according to the

crosshatch adhesion test method ASTM D3359. The resins werecoated onto aluminum plates at a thickness of 30 �m, 60 �m, 90 �mand 120 �m using a SHEEN Hand Coater and left at room tempera-ture for a week. A lattice pattern of cuts at right angle with similarspacing was made on the surface of the plates with the crosshatchcutter and commercial cellophane tape was applied over the lattice.

2.3.12. Impact strengthThe resins were coated at thicknesses of 30 �m, 60 �m, 90 �m

and 120 �m on aluminum plates which were then air-dried. Thesamples were subjected to the tubular impact tester model SHEENREF804. The maximum height of load with an indentor weight of2 lbs was identified as the impact resistance grade of the coating,where the film would not suffer physical damage.

2.3.13. Pencil hardness testThe test was done with an Erichsen scratch hardness test kit

(model 291) according to ASTM D3363-05 under room temperatureconditions and the hardest pencil grade from soft to hard (6B to 6H)that did not rupture or scratch the coating was termed the pencilhardness of the test specimens.

2.3.14. Water resistanceResins were coated on glass plates with the end sides was coated

with wax to prevent water absorption from open ends. The panelswere allowed to dry for 3 days. Plates were dipped in water for 24 h,and then water resistance was determined according to ASTM D1647-89.

2.3.15. Chemical resistanceThe chemical resistance of resins was determined on coated

glass plates that had been allowed to dry for 3 days. The plateswere immersed in alkali solution (2% NaOH), acid solution (2%H2SO4), hydrocarbon solvent (xylene) and polar solvent (acetone).Any changes in appearance were observed after 48 h.

3. Results and discussion

3.1. Structural elucidation and morphology

Monoglycerides based on palm oil, soy oil and sunfloweroil together with alkyd diols based on different monoglycerideswere successfully synthesized and confirmed by FTIR, 1H NMRspectroscopy and 13C NMR spectroscopy. Successful reactions ofphthalic anhydride with the three monoglycerides were appar-ent from the characteristic appearance of two troughs around1570–1600 cm−1. They indicated the presence of C C bonding ofthe aromatic ring of the phthalic anhydride component. A represen-tative of 1H NMR spectrum along with specific proton assignationsfor palm oil monoglyceride is also shown in Fig. 1. ı = 2.70 ppmwas attributed to CH CH CH of the polyunsaturated, linoleicacid constituent of palm oil monoglyceride whereas ı = 3.70 ppmwas attributed to the primary CH of the glycerol moiety of �-monoglycerides and ��′-monoglycerides as the minor alcoholysisby-product. In Fig. 2, the appearance of multiplet at 7.4–7.8 ppmindicated the aromatic proton from phthalic anhydride. The repre-sentative 13C NMR spectra of palm oil alkyd diol in Fig. 3 showedthe characteristic appearance of resonance peak attributed to thecarbonyl group attached to the phthalic anhydride constituentat ı = 165–169 ppm, whereas the carbonyl group for the mono-

glyceride moiety was seen at ı = 172 ppm. This implied successfulsynthesis of palm oil alkyd diol.

Successful syntheses of PAUs were also confirmed by FTIR.From the spectra (Fig. 4), no peak arising from NCO stretching

J.S. Ling et al. / Industrial Crops and Products 52 (2014) 74– 84 77

alm oi

(ttbcvP

Fig. 1. 1H NMR spectrum of p

at 2268–80 cm−1) was observed for all PAUs. This proved thathe isocyanate groups of MDI were fully reacted and absent inhese polymer products, whereas N H stretching of the urethaneond were portrayed by sharp peak around 3310–3340 cm−1. This

orrelated to the NH bending around 1597 cm−1 and stretchingibrations of urethane carbonyl groups ( C O) in all spectra ofAUs around 1650–1670 cm−1. The peak around 1730 cm−1 proved

Fig. 2. 1H NMR spectrum of palm

l monoglyceride in DMSO-d6.

the unaffected presence of C O (from ester linkages) from the pre-vious reaction between monoglycerides and phthalic anhydride.The peaks at 1510–1590 cm−1 also established the presence of aro-matic C C.

Successful synthesis of the PAUs resin was further corroboratedby the 1H NMR spectrum and 13C NMR spectrum in Figs. 5 and 6,respectively. Resonance at 8.0–9.5 ppm showed the presence of

oil alkyd diol in DMSO-d6.

78 J.S. Ling et al. / Industrial Crops and Products 52 (2014) 74– 84

Fig. 3. 13C NMR spectrum of palm oil alkyd diol in DMSO-d6.

Fig. 4. FTIR spectrum of (a) POPAU, (b) SOPAU, (c) SFPAU, (d) POSOPAU and (e) POSFPAU.

Table 1FTIR spectral data of monoglycerides, alkyd diols and poly(alkyd-urethane)s.

Functionalgroup

IR (cm−1)

PO-mono SO-mono SF-mono PO-diol SO-diol SF-diol POPAU SOPAU SFPAU POSOPAU POSFPAU

OH Broad 3407.14 Broad3407.16

Broad3418.14

Broad3459.04

Broad3445.42

Broad3445.76

– – – – –

C H aliphaticstretching

3006.09;2922.15;2852.16

3009.33;2925.68;2854.41

3008.43;2925.82;2854.72

3009.04;2924.47;2853.80

3007.63;2926.10;2854.73

3007.27;2925.82;2854.63

2925.25;2853.95

2924.78;2854.82

2923.70;2853.61

2925.12;2854.04

3006.96;2925.75;2854.38

>C O 1732.62 1742.51 1741.76 1738.74 1739.19 1738.60 1738.05 1730.34 1727.32 1739.70 1737.85Amide, C O

stretching– – – – – – 1664.22 1660.49 1660

overlap1641.17 1663.47

Ar C C – – – 1590.31;1590.10

1580.03;1550.49

1585.23;1553.93

1555.74;1540.67

1534.92;1520.76

1531.61;1519.49

1559.07;1511.08

1557.83;1511.79

NH stretch – – – – – – 3313.29 3333.59 3328.77 3314.56 3312.43N H bending – – – – – – 1597.67 1599.76 1598.49 1597.59 1597.79C N – – – – – – 1282.64 1259.99 1260.54 1283.02 1282.46

J.S. Ling et al. / Industrial Crops and Products 52 (2014) 74– 84 79

um of

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Fig. 5. 1H NMR spectr

NH proton in a urethane bond ( NH COO ). Peak at around.5 ppm which was previously assigned to the alkyd diol OH pro-on (Fig. 2) had disappeared in 1H NMR spectrum for PAU(Fig. 5)roved that all OH were successfully reacted. The multiplet signalst 7.0–7.5 ppm indicated the existence of aromatic protons fromDI component, which proved the occurrence of urethane linkage

o bond with diols in order to form the PAUs. In Fig. 6, the reso-ance at ı = 152 ppm proved the presence of carbonyl group of therethane linkage presented in the PAU. The other important char-

cteristic FTIR absorbance bands as shown in Table 1 also supporthe structures of components as per the reaction in Figs. 7 and 8.

The SEM micrographs of the alkyd-urethane systems gen-rally revealed homogeneous microstructures (Fig. 9). Soy oil

Fig. 6. 13C NMR spectrum o

POPAU in DMSO-d6.

based PAUs however seemed to have formed a more globu-lar structural geometry which could be due to entanglement ofmolecular chains and formation of higher level of inter- and intra-molecular bonding. The presence of homogenous morphology wasdue to the efficient crosslinking between PAU polymers, showingthat there was no phase-separation, which confirmed completereaction between alkyd and urethane components of the resinpolymer.

3.2. Physical properties and thermal analysis

Physical properties of the alkyd diols and PAUs synthesizedwhich included solubility and viscosity has been summarized in

f POPAU in DMSO-d6.

80 J.S. Ling et al. / Industrial Crops and Products 52 (2014) 74– 84

Fig. 7. Synthesis route of (a) palm oil monoglyceride and (b) palm oil alkyd diols.

Table 2Yield, physical characteristics, drying time and solubility of the synthesized alkyd diols and poly(alkyd-urethane)s.

Sample Yield(%)

Viscosity at25 ◦C (cPs)

Acid value (mgKOH/g sample)

Hydroxyl value(mg KOH/gsample)

Iodinenumber

Gel content(%)

Drying timea,b Solubilityc

4% 5% 6% DMF Toluene Ethanol THF Acetone

PO-diol 93 3578.3 4.09 135 – – – – – ++ ++ ++ ++ ++SO-diol 95 4098.4 3.85 130 – – – – – ++ ++ ++ ++ ++SF-diol 94 3987.0 4.57 133 – – – – – ++ ++ ++ ++ ++POPAU 82 14,976.0 – – 59.10 86.75 (±1.17) 96H 72H 48H ++ +− + + ++SOPAU 81 18,659.7 – – 139.56 98.10 (±0.25) 54H 48H 24H ++ +− + + ++SFPAU 85 17,989.8 – – 140.48 97.50 (±0.21) 48H 48H 24H ++ +− + + ++POSOPAU 88 16,758.3 – – 98.53 89.75 (±1.09) 72H 54H 48H ++ +− + + ++POSFPAU 83 17,235.1 – – 103.49 93.82 (±0.94) 54H 48H 48H ++ +− + + ++

a H, hours.b Cobalt content (% w/w).c ++, soluble at room temperature; +−, partially soluble; +, soluble on heating; −−, insoluble.

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Fig. 8. Synthesis route of poly(alkyd-urethane)s.

able 2. Viscosity data demonstrated that soy oil based PAU pos-essed the highest amount of crosslinks in polymers. Thus, theigher the amount of cross links meant formation of longer andore thoroughly branched polymer chains that led to more binding

ffect and therefore, higher viscosity.Major fatty acids presented in palm oil were the mono-

aturated, oleic fatty acid, 45% and the saturated fatty acids,almitic acid, 39% while soy oil was consisted of mainly polyun-aturated, linoleic acid (53%), followed by monounsaturated, oleiccid (23.4%) and saturated, palmitic acid (11%) (Guner et al., 2006;antzaris, 2010). Sunflower oil on the other hand was reported toossess mainly linoleic acid, 47% and oleic acid, 42%. With a higherroportion of saturated bonds compared to other oils, palm oilxhibited the resultant PAUs with lower degree of crosslinks, thusower viscosity. Palm oil based PAU also had more aliphatic carbonhain in their fatty acid structures, which gave much lower flowingesistance as compared to the other PAUs.

Gel content refers to the degree of curing that occurs for eachAU. From the result in Table 2, all synthesized PAUs had highegree of curing which was above 91% except for palm oil basedAU and palm-soy based PAU. Gel content was directly proportion-te to the amount of double bonds present in each composition. Theigher amount of double bonds presented in the fatty acid compo-itions of soy oil PAU and sunflower oil PAU gave highest degree ofrosslink at 98.10% with STDEV of 0.25 and 97.50% with STDEV of.21, respectively, followed by palm-sunflower oil based PAU andalm-soy based PAU. This coincided with the observations whereoy oil and sunflower oil based PAUs showed the highest reading of39.56 and 140.48, respectively, in the iodine number test whichas to determine the amount of double bonds presented in each

AUs.From the drying time tests, it was also observed that soy oil

AU and sunflower oil PAU took the shortest time to dry due tohe lower proportion of saturated fatty acid chains compared to

d Products 52 (2014) 74– 84 81

palm oil. As expected, this was followed by palm-sunflower based,palm-soy based and palm oil based PAU as drying time dependedon the original polymer viscosity and unsaturations (Guner et al.,2002). It was reported that alkyd based on palm oil took up toan average of 8 days to dry (Issam and Cheun, 2009) whereaspalm oil PAU in this study took up to 4 days. Therefore, we canclaim that the presence of urethane linkage within the alkydbackbone had given stronger intermolecular interaction due tothe stronger hydrogen-bonding capabilities, which led to shorterdrying time. It was observed that higher amount of catalyst alsodramatically decreased drying time of the PAUs as this acceleratedthe oxygen uptake either at the double bonds or at the methylenegroups of fatty acid chains in the poly(alkyd-urethane)s duringthe autoxidization process. (Akintayo and Adebowale, 2004b). Thesolubility of a polymer is a significant factor for uniform curingduring film forming and application. Solvents are normally addedinto resins to resolve the problem of high viscosity resins, whichis an obstacle in wettability on substrates. The PAUs showed muchsimilarity in solubility, which was partially soluble in differenttypes of solvents except in DMF and acetone where they were fullysoluble.

Thermogravimetric analysis (TGA) of PAU in Fig. 10 revealedthat the decomposition of the samples were slow and gradual withthe same pattern of degradations. They consisted of three domi-nant steps corresponding to the first, second and third degradationsteps of PAU at around 290 ◦C, 390 ◦C and 430 ◦C, respectively. Theinitial degradation temperature was dependent upon the thermalstability of the weakest point in the polymer structure (Krol, 2007).The most thermoliable portion within the structure was referredto be the aliphatic long chain of fatty acid from the monoglyceridecomponent thus the first step was associated to the polymer chainsscission and fatty acid aliphatic chain degradation in PAU sample.The second step corresponded to the decomposition of urethanelinkages while the third step was due to the decomposition ofmost thermostable unit – the aromatic moieties and ester groupof the alkyd component. It was noticed that all synthesized poly-mers possessed a relatively high thermal stability with the onsetof decomposition occurring at around 270 ◦C. Soy oil PAU gave thehighest thermal stability with the initial decomposition temper-atures of 290 ◦C, followed closely by sunflower oil PAU at 284 ◦Crespectively which coincided with their homogenous morphology.This may be due to the presence of polyunsaturated fatty acid chainin the alkyd constituent, which in turn promoted higher amountof crosslinks as compared to palm oil PAU. Palm oil PAU gave thelowest thermal stability with the onset of degradation at around270 ◦C. The relatively inferior thermal stability associated to palmoil PAU may be due to the lack of unsaturated bonding in the palmoil fatty acid chain that led to a lower degree of crosslinks. How-ever, it was also observed that by imparting soy oil or sunfloweroil based alkyd diols, thermal stability of the PAU based on palmoil was significantly increased. Furthermore, at around 800 ◦C, theTGA curves indicated complete de-crosslinking and thermal degra-dation of the PAU with the highest weight residue of 55% (Soy oilPAU) followed by 41% (Palm-sunflower PAU) and 37% (Palm OilPAU, Sunflower oil PAU and Palm-soy PAU) respectively. It wasalso reported that the decomposition of urethane moieties startedbetween 150 ◦C and 200 ◦C but this may vary depending on thetype of substituents on the isocyanate and polyol sections andthe decomposition of urethane bondings occurred through dis-sociation. Thus, as a consequence, led to the formation of threegroups of products; 1-isocyanate and alcohol, 2-primary aminesand olefins and 3-secondary amines (Janvi et al., 2000). Thus far, itwas inferable that the presence of alkyd backbone had potentiallyincreased the thermal stability of the PAU produced. Table 3 sum-

marizes the characteristic temperature for thermal degradations ofPAU.

82 J.S. Ling et al. / Industrial Crops and Products 52 (2014) 74– 84

Fig. 9. SEM images of poly(alkyd-urethane)s: (a) POPAU, (b

Table 3Characteristic temperature of thermal degradations of poly(alkyd-urethane)s.

Sample T5a (◦C) T10

b (◦C) T20c (◦C) Residual weightd

(wt. %)

POPAU 270 311 368 37SOPAU 292 341 403 55SFPAU 284 331 376 37POSOPAU 287 328 377 37POSFPAU 286 332 377 41

a T5 temperature of 5% weight lost.

3

aIbtt

b T10 temperature of 10% weight lost.c T20 temperature of 20% weight lost.d Residual weight at 800 ◦C.

.3. Mechanical properties and chemical resistance

It was designed in such a way that fatty acid chains, esternd urethane linkages rendered a complete PAU coating system.

n addition, hydrogen bondings (between PAU chains as well asetween the polymers and substrate) were involved in the sys-em and collectively influencing the mechanical performance ofhe coating. As it is shown from the results in Table 4, all of the

) SOPAU, (c) SFPAU, (d) POSOPAU, and (e) POSFPAU.

synthesized PAUs exhibit good adhesion properties. It was reportedthat adherence of a polymer to a substrate is related to the inherentchemical structure and its flexibility (Shailesh et al., 2008) and thus,it was deduced that the mentioned linkages and hydrogen bondinghad helped form an infusible thermoset and well-adhered coat-ing. The PAUs also possessed comparatively good impact resistanceand hardness. Sunflower oil PAU possessed the highest readings inimpact resistance and pencil hardness. By order of superiority, sun-flower oil PAU was followed closely by soy oil PAU, palm-sunflowerPAU, palm-soy PAU and palm oil PAU. This can be attributed to thepresence of urethane linkage and ester linkage in the chains of poly-mers that provided flexibility while the aromatic composition ofthe polymer gave the hardness property. The loosening and subse-quent reconstitution of acyclic and cyclic intermolecular hydrogenbridge bonds also served to an extent in protecting the covalentpolymer chains until a force high enough to cause any irreversibledamage to the polymer chain, thus contribute to good impact resis-

tance and hardness (Stoye et al., 1996). It was also observed that asthe thickness of the film increased, the impact resistance and hard-ness also increased. Good hardness of film generally related to theextent of the polymeric crosslinking (Shailesh et al., 2008). With

J.S. Ling et al. / Industrial Crops and Products 52 (2014) 74– 84 83

kyd-u

harms

s

TM

Fig. 10. TG and DTG curves of poly(al

igher crosslinkings, films were generally harder, more durablend tougher (Turner, 1980, 1988). Thus, the observations acquiredegarding the overall mechanical performances are in good agree-

ent with the high thermal stability and the gel content of the

ynthesized PAU.It was observed that the coated films were affected with

ome swelling in the NaOH resistance test. The presence of ester

able 4echanical properties and chemical resistance of poly(alkyd-urethane)s.

Sample Cross hatch adhesion testa Impact resistance (in.)

30 �m 60 �m 90 �m 120 �m 30 �m 60 �m 90 �m 120 �m

POPAU 4B(2%)

3B(6%)

3B(5%)

4B(3%)

15 18 20 21

SOPAU 4B(3%)

4B(1%)

3B(7%)

4B(4%)

18 20 23 24

SFPAU 4B(2%)

4B(1%)

4B(3%)

4B(1%)

19 20 24 25

POSOPAU 3B(8%)

4B(3%)

3B(8%)

3B(9%)

21 22 24 25

POSFPAU 3B(6%)

4B(3%)

4B (4%) 4B(4%)

20 22 23 25

a 5B: 0% area removed; 4B: less than 5% area removed; 3B: 5–15% area removed; 2B: 15b a, unaffected; b, film swell; c, film crack and slightly removed.

rethane)s at heating rate 10 ◦C min−1.

linkages caused slight depolymerizations in the alkyd backbones ofthe resin. Small wrinkles were also observed as arising from partsof the polymer with lower crosslink density due to the crosslink-

ing mechanism between carbon fatty acid polymeric side chains.Water and acid resistance of a resin are very important in coatingto ensure high coating durability. Generally, PAUs were unaffectedby the acidic solution after 12 h of application. However, PAU films

Pencil hardness Chemical resistance testsb

120 �m NaOH (2%,w/w)

H2SO4(2%,w/w)

H2O Xylene Acetone

5B b b a b c

B b a a b c

HB b a a b c

4B b a a b c

B b a a b c

–35% area removed; 1B: 35–65% area removed; 0B: greater than 65% area removed.

8 ops an

bAtIadtsgobp

4

dhibtrtPiao

A

t(

R

A

A

A

A

A

A

C

D

G

G

H

H

USDA, 2013b. United States Department of Agriculture. “Table 03: Major Veg-

4 J.S. Ling et al. / Industrial Cr

ased on palm oil showed slight swelling and blush after 24 h.s shown in Table 4, all three resins possessed good water resis-

ance. The coated films showed no change after 24 h of immersion.n non-polar solvent such as xylene, the resistance of resins wascceptable where slight swelling were observed in all PAU filmsue to the polar groups in the resins. All PAU showed poor resis-ance in polar solvent (acetone) where the films cracked and werelightly removed. However, generally the PAU possessed relativelyood chemical resistance and such can be correlated to the presencef optimum urethane linkages, stable inter-polymeric hydrogenonding of the urethane moieties and well adhered coating thatrevent corrosive ions to penetrate into the coating.

. Conclusion

FTIR and 1H NMR spectroscopy revealed that the novel alkydiols and poly(alkyd-urethane)s based on different vegetable oilsave been successfully synthesized with good surface homogene-

ty. Sunfloweroil based PAUs displayed drying superiority, followedy soy oil, mixed oil based PAUs and palm oil based PAU. In general,he PAUs exhibited good mechanical performances and chemicalesistance. This study revealed that the adopted technique of usinghe selected sources of vegetable oil in the novel chemical design ofAUs created a potential alternative reaction schemes to be appliedn the industry for surface coating, binder for composites and otherpplications, thus aiding the effort to replace or minimize the usef non-sustainable petroleum-based raw material.

cknowledgement

The authors would like to thank Universiti Sains Malaysia forhe financial support provided through short term research GrantNo.: 304/PTEKIND/6311031).

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